The present invention relates to testing of radio frequency (RF) signal receivers, and in particular, to measuring input signal power sensitivities of RF signal receivers under low input signal power conditions using received signal strength indicator (RSSI) functions.
Many of today's electronic devices use wireless signal technologies for both connectivity and communications purposes. Because wireless devices transmit and receive electromagnetic energy, and because two or more wireless devices have the potential of interfering with the operations of one another by virtue of their signal frequencies and power spectral densities, these devices and their wireless signal technologies must adhere to various wireless signal technology standard specifications.
When designing such wireless devices, engineers take extra care to ensure that such devices will meet or exceed each of their included wireless signal technology prescribed standard-based specifications. Furthermore, when these devices are later being manufactured in quantity, they are tested to ensure that manufacturing defects will not cause improper operation, including their adherence to the included wireless signal technology standard-based specifications.
Testing of such wireless devices typically involves testing of the receiving and transmitting subsystems of the device under test (DUT). The testing system will send a prescribed sequence of test data packet signals to a DUT, e.g., using different frequencies, power levels, and/or signal modulation techniques to determine if the DUT receiving subsystem is operating properly. Similarly, the DUT will send test data packet signals at a variety of frequencies, power levels, and/or modulation techniques for reception and processing by the testing system to determine if the DUT transmitting subsystem is operating properly.
For testing these devices following their manufacture and assembly, current wireless device test systems typically employ testing systems having various subsystems for providing test signals to each device under test (DUT) and analyzing signals received from each DUT. Some systems (often referred to as “testers”) include at least a vector signal generator (VSG) for providing the source signals to be transmitted to the DUT, and a vector signal analyzer (VSA) for analyzing signals produced by the DUT. The production of test signals by the VSG and signal analysis performed by the VSA are generally programmable (e.g., through use of an internal programmable controller or an external programmable controller such as a personal computer) so as to allow each to be used for testing a variety of devices for adherence to a variety of wireless signal technology standards with differing frequency ranges, bandwidths and signal modulation characteristics.
During manufacturing testing, it is common to test a partially assembled device using conductive signal connections and conveyance (e.g., co-axial RF cables and connectors) and test systems designed for such hardware. However, final testing of fully assembled devices designed for wireless operations typically requires over-the-air (OTA) signal paths and conveyance which present very different signal levels as compared to wired systems. For example, wireless signal levels are typically much lower than those conveyed conductively. This may require signal boosting adjuncts in the test system front end. In addition, test systems which ordinarily process signal levels that are considerably higher may have inherent noise levels that are small compared to conducted signals but proportionally higher when compared to wireless signals and, therefore, more likely to be disruptive when testing OTA signals.
Wireless devices themselves are designed to receive small signals and often have received signal strength indication (RSSI) subsystems that can work with the low-level signals encountered during OTA operations. However, most such RSSI subsystems have lower, often significantly lower, resolution than subsystems used to measure power of conducted signals. Thus, although RSSI functionality may be employed to measure power of OTA signals, the resolution may not be sufficient to instill confidence in results when using OTA test techniques.
Accordingly, it would be advantageous to enable use of existing RSSI subsystems while somehow overcoming their low signal level constraints and provide sufficient resolution to make more accurate power-level measurements, thereby enabling testing low-level signal power at lower test device cost without compromising testing integrity.